This invention relates to test systems, and more particularly to production-line D.C. testing of memory modules.
Memory is a basic part of many kinds of electronic systems. A common, low-cost memory is dynamic-random-access memory (DRAM). Rather than sell individual DRAM chips, such chips are often pre-assembled into modules that can be inserted into sockets in a wide variety of systems. Such memory modules have gained enormous popularity in recent years. Most personal computers (PC""s) are shipped with sockets for memory modules so the PC user can later add additional modules, increasing the memory capacity of the PC. High-volume production and competition have driven module costs down dramatically, benefiting the PC buyer.
Memory modules are made in many different sizes and capacities, such as older 30-pin modules and newer 72-pin and 168-pin modules. The xe2x80x9cpinsxe2x80x9d were originally pins extending from the module""s edge, but now most modules are leadless, having metal contact pads or leads. The modules are small in size, being about 3-5 inches long and about an inch to an inch and a half in height.
The modules contain a small printed-circuit board substrate, typically a multi-layer board with alternating laminated layers of fiberglass insulation and foil or metal interconnect layers. Surface mounted components such as DRAM chips and capacitors are soldered onto one or both surfaces of the substrate. Memory modules are often manufactured in large automated machines using surface-mount-technology (SMT). These machines are like small assembly lines, producing finished but untested memory modules. The memory modules are then tested before shipment.
The highly-competitive, high-volume nature of the memory-module-manufacturing business dictates that costs be driven as low as possible. Testing costs are significant. Methods to reduce test cost or complexity are desirable.